ford taurus 2000, coolant disapears n oil over flows, changed water pump and thermostat followed by coolant flush, whats my problem?

is the overflow/return tube mounted in/near the cap there? if this one falls off, there will be no return and expansion will "blow the lid" off the expansion tank~....and starve of coolant too....this return line is important~

i believe that at this point theirs no visible leaks all coolant hoses are fine and connected